Semiconductor device

ABSTRACT

Provided is a semiconductor device, such as a RFID tag, which receives and transmits data wirelessly and generates electric power using carrier waves, where the semiconductor device is configured to generate a desired power supply voltage even when the power of the carrier waves is insufficient. The semiconductor device comprises a storage capacitor portion formed of a plurality of capacitor portions, where the plurality of capacitor portions are charged in the state of parallel connection, and a high voltage is extracted from part of or all of the plurality of capacitor portions by interconverting the parallel connection to a series connection when a circuit in the semiconductor device is operated. Accordingly, even when the power of carrier waves is reduced a voltage that is necessary for the circuit operation can be assured.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a semiconductor device thatcommunicates wirelessly.

2. Description of the Related Art

In recent years, an individual identification technique which employswireless communication with an electromagnetic field, radio waves, orthe like has attracted attention. In particular, an individualidentification technique which employs an RFID (radio frequencyidentification) tag as a semiconductor device which communicates datavia wireless communication has attracted attention. An RFID tag(hereinafter simply referred as an RFID) is also referred to as an IC(integrated circuit) tag, an IC chip, an RF tag, a wireless tag, and anelectronic tag. An individual identification technique which employs anRFID is beginning to be made use of in production, management, and thelike of individual objects, and it is expected that this technique willalso be applied to individual authentication.

The RFIDs can be divided into two types: an active type RFID tag havinga built-in power supply that is necessary for the circuit operationaccompanied with reception and transmission data between the tag and areader/writer, and a passive type RFID tag driven with generatingelectric power in the tag using electric power of radio waves orelectromagnetic waves (carrier waves) from the outside (regarding theactive type, see Reference 1: Japanese Published Patent Application No.2005-316724, and regarding the passive type, see Reference 2: JapaneseTranslation of PCT International Application No. 2006-503376). Theactive type RFID has a built-in power supply for driving the RFID, andincludes a battery as the power supply. Meanwhile, in the passive typeRFID, electric power for driving the RFID is made by using electricpower of radio waves or electromagnetic waves (carrier waves) from theoutside. Therefore, the passive type RFID has a structure which does notinclude a battery.

SUMMARY OF THE INVENTION

As shown in FIG. 2, in a passive RFID tag, an antenna 204 in an RFID tag203 receives alternating carrier waves 202 which is supplied from areader/writer 201 to generate an AC voltage, the AC voltage is convertedinto a direct voltage by a rectifier circuit portion 205 to generateelectric power, and further, electric charge is stored in a storagecapacitor portion 206, so that the electric power serves as the powersupply for driving a function portion 207 in the RFID tag 203.

However, there is a problem that when the rectifier circuit portion 205converts an AC voltage into a DC voltage, not a small loss is caused. Inaddition, when a high voltage is desired to be obtained in a tag, thereceived power of carrier waves needs to be heightened, however, therelationship between the received power and the distance between a tagand a reader/writer is trade-off. Further, in the case where thereceived power of carrier waves are sufficiently high, countermeasuressuch as the thickening of an insulating film and the like are neededbecause the transistor included in the rectifier circuit portion 205 isrequired to have withstand voltage corresponding to the level of thereceived power. However, in using such a transistor, when the receivedpower of carrier waves is reduced, specifically the distance between thetag and the reader/writer increases, a defect that enough voltage is notgenerated occurs.

Applications of an RFID tag are not only a tag which is required toconduct reception or transmission in a contact state with areader/writer because of a security reason like a advanced freightsystem of railway (such as SUICA (registered trademark)) or the like,but also a tag which is required to have an increased communicationdistance between the tag and the reader/writer. In order to increase thecommunication distance, not surprisingly enough voltage for the circuitoperation inside the tag should be generated, even if the tag is in thecondition that the received power of carrier waves is low.

In view of the foregoing problems, it is an object of the presentinvention to provide a semiconductor device which can generate desiredlevel of a power supply voltage even when the received power of carrierwaves is reduced.

One feature of a semiconductor device of the present invention is toinclude an antenna which generates an AC voltage by receivingalternating carrier waves, a rectifier circuit which generates a DCvoltage from the AC voltage, and a storage capacitor portion whichstores the generated DC voltage. The storage capacitor portion includesa plurality of capacitor elements and a plurality of switch meansprovided between electrodes of the plurality of capacitor elements. Onor off of each the plurality of switch is controlled so that switchingbetween a first mode in which all the plurality of capacitor elementsare connected in parallel and a second mode in which part or all theplurality of capacitor elements are connected in series is performed.

One feature of a semiconductor device of the present invention is toinclude an antenna which generates an AC voltage by receivingalternating carrier waves, a rectifier circuit which generates a DCvoltage from the AC voltage, a storage capacitor portion which storesthe generated DC voltage, and a function portion which conductprocessing in response to a command which is included in the receivedcarrier waves. The storage capacitor portion includes a plurality ofcapacitor elements and a plurality of switch means provided betweenelectrodes of the plurality of capacitor elements. On or off of theplurality of switches means is controlled so that switching between afirst mode in which all the plurality of capacitor elements areconnected in parallel and a second mode in which part or all theplurality of capacitor elements are connected in series is performed. Ina period when an electric charge is accumulated in the storage capacitorportion, the first mode is taken, and in a period when the functionportion is driven by the electric charge accumulated in the storagecapacitor portion, the second mode is taken.

In the foregoing semiconductor device of the present invention, therectifier circuit, the storage capacitor portion and the functionportion may be formed using a thin film transistor.

One feature of a semiconductor device of the present invention is toinclude an antenna which generates an AC voltage by receivingalternating carrier waves, a rectifier circuit which generates a DCvoltage from the AC voltage, first and second storage capacitor portionwhich stores the generated DC voltage, first function portion whichconducts processing in response to a command which is included in thereceived carrier waves, and a second function portion requiring adriving voltage higher than that of the first function portion. Thesecond storage capacitor portion includes a plurality of capacitorelements and a plurality of switches means provided between electrodesof the plurality of capacitor element. On or off of the plurality ofswitches means is controlled so that switching between a first mode inwhich all the plurality of capacitor elements which the second storagecapacitor portion includes are connected in parallel and a second modein which part or all the plurality of capacitor elements which thesecond storage capacitor portion includes are connected in series isperformed. Electric power obtained from the first storage capacitorportion is used for driving of the first function portion, and electricpower obtained by switching the second storage capacitor portion to bein the second mode is used for driving of the second function portion.

In the foregoing semiconductor device of the present invention, therectifier circuit, the first storage capacitor portion, the secondstorage capacitor portion, the first function portion, or the secondfunction portion may be formed of a thin film transistor.

Further, in the foregoing semiconductor device of the present invention,a rewritable memory element group or the like may be used for the secondfunction portion.

By a semiconductor device of the present invention, in a storagecapacitor portion formed of a plurality of capacitor elements, theplurality of capacitor elements are charged in the state of parallelconnection, and at the circuit operation, a high voltage can be takenout by connecting part or all the plurality of capacitor elements inseries corresponding to a power supply voltage in need at that time.Accordingly, when the received power of carrier waves is reduced, i.e.even when a distance between a tag and a reader/writer becomes large, avoltage that is necessary for the circuit operation inside the tag canbe assured, which greatly contributes to increase of a communicationdistance.

Additionally, circuit group that requires a high voltage for theoperation and could not be incorporated conventionally can beincorporated in the tag, which greatly contributes to high functional ofthe tag.

BRIEF DESCRIPTION OF THE DRAWINGS

In the accompany drawings:

FIGS. 1A to 1C are diagrams illustrating a structure and generaloperations of a semiconductor device which is one embodiment mode of thepresent invention;

FIG. 2 is a diagram illustrating a structure of an RFID tag and areader/writer;

FIG. 3 is a diagram illustrating a structure of a reader/writer and anIC card which use a semiconductor device of one embodiment mode of thepresent invention;

FIG. 4A to 4D are diagrams illustrating an exemplary manufacturingprocess of a semiconductor device of the present invention;

FIGS. 5A and 5B are diagrams illustrating an exemplary manufacturingprocess of a semiconductor device of the present invention;

FIGS. 6A and 6B are diagrams illustrating an exemplary manufacturingprocess of a semiconductor device of the present invention; and

FIG. 7 is a diagram illustrating a structure of a semiconductor device,which is one embodiment mode of the present invention.

EMBODIMENT MODE 1

Embodiment modes of the present invention will be explained hereinafterwith reference to the drawings. Note that the present invention is notnarrowly limited to the description below, and it is easily understoodby those skilled in the art that various changes and modifications canbe made in forms and details without departing from the spirit and thescope of the present invention. Accordingly, the present inventionshould not be construed as being limited to the content of theembodiment modes below. Note that in structures of the present inventionto be described below, there are cases where like reference numeralsdenoting like portions in different drawings are used in common.

The frequency of carrier waves used for transmission or receptionbetween a tag and a reader/writer is 125 kHz, 13.56 MHz, 915 MHz, 2.45GHz, or the like, which are set by ISO standards or the like. Of course,the frequency of carrier waves transmitted or received between anantenna and a reader/writer is not limited to this, and for example, anyof the following frequencies can also be used: 300 GHz to 3 THz, whichis a submillimeter wave, 30 GHz to 300 GHz, which is a millimeter wave,3 GHz to 30 GHz, which is a microwave, 300 MHz to 3 GHz, which is anultrahigh frequency wave, 30 MHz to 300 MHz, which is a very highfrequency wave, 3 MHz to 30 MHz, which is a high frequency wave, 300 kHzto 3 MHz, which is a medium frequency wave, 30 kHz to 300 kHz, which isa low frequency wave, or 3 kHz to 30 kHz, which is a very low frequencywave.

As a method of modulating the carrier waves, analog modulation ordigital modulation may be used. Amplitude modulation, phase modulation,frequency modulation, or spread spectrum may also be used. Preferably,amplitude modulation or frequency modulation is used.

There are no limitations, in particular, on the shape of the antennathat can be used in the present invention. Therefore, an electromagneticcoupling method, an electromagnetic induction method, an electromagneticwave method, an optical method, or the like can be used as atransmission method. The practitioner may select the transmissionmethod, as appropriate, in consideration of the intended use, and anantenna with the most appropriate length and shape for the transmissionmethod may be provided. An electromagnetic wave method can be used forthe signal transmission method in the present invention, and further, amicrowave method can be used, as well.

In a case where an electromagnetic coupling method or an electromagneticinduction method (for example, 13.56 MHz band) is applied as atransmission method, electromagnetic induction by change of the electricfield density is utilized; therefore, a conductive film serving as anantenna is formed into a circular shape (such as a loop antenna) or aspiral shape (such as a spiral antenna).

In a case where a microwave method (for example, UHF band (860 to 960MHz band), 2.45 GHz band, or the like), which is one of theelectromagnetic wave methods, is applied as the transmission method, alength or a shape of a conductive film serving as an antenna may beselected as appropriate in consideration of a wavelength of an electricwave used for signal transmission. For example, the conductive filmserving as an antenna can be formed into a linear shape (such as adipole antenna), a flat shape (such as a patch antenna), or the like.Further, the shape of the conductive film serving as an antenna is notlimited to the linear shape, and the conductive film may be formed intoa curve shape, a meandering shape, or a combined shape thereof inconsideration of a wavelength of an electromagnetic wave.

FIG. 1A shows one embodiment mode of the present invention. Here, anRFID tag is described as a typical example of a semiconductor device ofthe present invention. This RFID tag 203 includes the antenna 204, therectifier circuit portion 205, the storage capacitor portion 206, andthe function portion 207. The storage capacitor portion 206 is dividedinto a plurality of capacitor elements 101 to 106. Each switch 107 isprovided between electrodes of the capacitor elements 101 to 106. Inaddition, a switch 108 may be provided between the rectifier circuitportion 205 and the storage capacitor portion 206, and a switch 109 maybe provided between the storage capacitor portion 206 and the functionportion 207.

On or off of each the switch 107 which is provided between eachelectrode of the capacitor elements 101 to 106 is controlled to be in anintended state, so that the connection state of the capacitor elements101 to 106 can be switched. The embodiment is specifically describedbelow.

FIG. 1B shows a state that all the capacitor elements 101 to 106 areconnected in series. At this time, the capacitor elements 101 to 106have capacitances c1 to c6 respectively. For simple description, here,the capacitances are assumed to have the following relationship:c1=c2=c3=c4=c5=c6. The rectifier circuit rectifies an AC voltage toobtain a DC voltage. At this time, since the capacitor elements 101 to106 are connected in series, a voltage V is stored in the storagecapacitor portion 206 having a total capacitance C=c1+c2+c3+c4+c5+c6.

In a state of the capacitor elements 101 to 106 connected in series, thevoltage V is used for driving of another circuit, as a DC power supplyat discharge.

On the other hand, a connection state of the capacitor elements 101 to106 is changed from the state shown in FIG. 1B to a state shown in FIG.1C by switching on or off each the switch 107. At this time, thecapacitor elements 101 to 106 are connected in series, and the voltage Vis stored in each of the capacitor 106 to 109 having capacitances c1,c2, c3, c4, c5, and c6. Therefore, when discharge begins with thisstate, the voltage V can be used as a DC power supply six times of thevoltage V. Of course, since the total amount of charge C does not changefrom the time of discharge in the state of FIG. 1B, a current value thatcan be obtained becomes ⅙. Thus, although a period that sufficientvoltage is stored for driving a circuit becomes shorter than that ofFIG. 1B, driving of a circuit which requires a higher driving voltagebecomes possible.

On the other hand, when the received power of carrier waves from areader/writer, that is, when the rectifier circuit portion 205 can notoutput a sufficient voltage and the voltage Vat the storage capacitorportion 206 is not enough, a sufficient voltage can be obtained for thecircuit operation by this method. For example, in the case of an RFIDtag or the like, a voltage is only required to be assured when data isreceived or transmitted; therefore the RFID tag works well even thoughthe period when voltage can be stored is short.

As to controlling the switches 108 and 109, for example in FIG. 1A,there is a method in which a potential of a node which is high potentialside of the storage capacitor portion 206 is obtained to be comparedusing a comparator or the like, and part or all the capacitor elements101 to 106 are switched to be connected in series when the potential isunder a certain potential, or the like. Since the potential of the nodewhich is high potential side of the storage capacitor portion 206increases by part or all the capacitor elements 101 to 106 beingconnected in series, a countermeasure, in which a portion obtaining thepotential is interrupted so as not to return to the parallel connectionimmediately, or the like is necessary.

Note that as to the switches 108 and 109, when the capacitor elements101 to 106 are used in parallel connection regardless in charging ordischarging, the switches may always turns on. However, when capacitorelements 101 to 106 are used in series connection in discharging andelectric power is needed to be supplied, it is preferable when chargingis performed, the switch 108 turns on, and the switch 109 turns off sothat the function portion 207 is disconnected, and when discharging isperformed, the switch 108 turns off, and the switch 109 turns on so thatthe rectifier circuit portion 205 is disconnected.

Here, description is made with the assumption each capacitance of thecapacitor elements 101 to 106 is equal; however, the present inventionis not limited to this. In addition, in this embodiment mode,connections of all the plurality of the capacitor elements 101 to 106are switched by the switches; however, a structure may be employed, inwhich only part of the capacitor elements connected in series are usedfor supplying electric power for a high-voltage driving portion, and theother capacitor elements connected in parallel or a single capacitorelement are used for supplying electric power for a low-voltage drivingportion.

Additionally, although not shown in FIGS. 1A to 1C, additional storagecapacitor portion may be provided in parallel with the storage capacitorportion 206, as a power supply for driving the switches 107, whichcontrols connections of the capacitor elements 101 to 106, and theswitches 108 and 109.

EMBODIMENT MODE 2

This embodiment mode will describe an exemplary structure of an IC cardusing a semiconductor device of the present invention, with reference toFIG. 3.

An IC card 300 having an RFID tag conducts reception and transmission ofdata between a reader/writer 301 and the IC card 300 using the carrierwaves 302 which has a frequency corresponding to various standards. Thecarrier waves 302 which are output from the reader/writer 301 are inputto a resonant circuit 304 which has an antenna 303. The resonant circuit304 has a rectifier circuit, a storage capacitor, and the like, and a DCvoltage is generated from an AC voltage, which is generated by receptionof the carrier waves 302, using the rectifier circuit. The storagecapacitor smoothes and stores the generated DC voltage.

The AC voltage which is generated by reception of the carrier waves 302is input to a clock generation circuit 305, and the clock generationcircuit 305 generates a clock signal having a desired frequency byfrequency dividing or the like, and supplies the clock signal fordriving an internal circuit.

In addition, the carrier waves 302 include data, that is sent to the ICcard 300, in the state that the amplitude, frequency, or the like of thecarrier waves 302 is modulated. The data is demodulated to a digitalsignal by a modulation/demodulation circuit 306. Additionally, themodulation/demodulation circuit 306 has a function for modulating adigital signal to be output on the carrier waves 302 when the IC card300 responds to the reader/writer 301.

A dotted frame 307 is a functional circuit portion having a logiccircuit 308 which processes a command inside, a mask ROM portion 309which stores a unique ID of the IC card or the like, and a rewritablememory portion 310 which enables information to be updated.

The rewritable memory portion 310 is preferably a memory, which canwrite or read information by receiving a command from the reader/writer301. In addition, the rewritable memory portion 310 is preferably amemory, which can write/erase information electrically like an EEPROM,because nonvolatility for storing information in a period, in which asignal from the reader/writer 301 is not received, is required. Since anEEPROM requires a relatively high power supply voltage in writing, byusing the semiconductor device of the present invention, a voltage,which is higher than the usual DC voltage and is obtained by rectifyingan AC voltage which is generated by reception of the carrier waves 302can be obtained, and writing can be achieved.

In this case, as well as Embodiment Mode 1, by control of the switches108 and 109 illustrated in FIG. 1A, part or all the capacitor elements101 to 106 in the storage capacitor portion 206 are connected in series,so that high potential is obtained. In this embodiment mode, theswitches 108 and 109 may be controlled by using a signal serving as aflag for starting the writing operation to the rewritable memory portion310.

On the other hand, in the case where the RFID tag 203 has no portionwhich requires a higher driving voltage than the peripheral of thefunction portion does, when the received power of the carrier waves froma reader/writer is reduced, that is, when the rectifier circuit portion205 shown in FIG. 2 can not output enough voltage, and the storagecapacitor portion 206 can not obtain the sufficient voltage V, enoughvoltage for the circuit operation can be obtained using a semiconductordevice of the present invention.

Note that for the storage capacitor provided in the resonant circuit304, as shown in FIG. 7, a first storage capacitor portion 701 that isused only in a state of normal parallel connection and a second storagecapacitor portion 702 that can be switched between parallel connectionand series connection are mounted separately. After both the storagecapacitor portion 701 and 702 are charged by a rectifier circuit 700,with the structure of the storage capacitor portion 701 and 702 beingcompletely separated, the first storage capacitor portion 701 may beused as a power supply for driving of the logic circuit 308 and forreadout of the mask ROM portion 309, and the second storage capacitorportion 702 may be used for supplying writing power to the rewritablememory portion 310. The storage capacitor portion 701 and 702 areseparated completely, so that driving of the logic circuit 308 andreading of the mask ROM portion 309 can be conducted stably in parallelwith writing to the rewritable memory portion 310.

Alternatively, when driving of the logic circuit 308, and reading of themask ROM portion 309 and the rewritable memory portion 310 areconducted, the plurality of capacitor elements in the second storagecapacitor portion 702 in parallel connection is combined with the firststorage capacitor portion 701 to supply electric power. When writing tothe rewritable memory portion 310 is needed, the plurality of capacitorelements in the second storage capacitor portion 702 is connected inseries to ensure and supply a writing voltage, and the first storagecapacitor portion 701 in parallel connection may supply electric powerfor driving of the logic circuit 308 and for readout of the mask ROMportion 309.

EMBODIMENT 1

This embodiment will describe an exemplary manufacture method of asemiconductor device shown in the above embodiment modes, with referenceto diagrams. Here, the case is described that elements, included in acircuit such as an analog portion or the like which has a functionportion, a rectifier circuit, a power supply circuit, and the like, areprovided over one substrate using thin film transistors. Additionally,the case is described that a capacitor element of a thin film transistortype is provided as a power storage element. Of course, a structureprovided with a small secondary battery instead of a capacitor elementof a thin film transistor type can be employed.

First, an insulating film 1304 serving as a base film and asemiconductor film 1305 (for example, a film containing an amorphoussilicon) are stacked and formed over one surface of a substrate 1301(see FIG. 4A). Note that the insulating film 1304 and the semiconductorfilm 1305 can be formed consecutively.

The substrate 1301 is selected from a glass substrate, a quartzsubstrate, a metal substrate such as a stainless steel substrate or thelike, a ceramic substrate, a semiconductor substrate such as a Sisubstrate or the like, a silicon on insulator (SOI) substrate, or thelike. Alternatively, as a plastic substrate, a substrate of polyethyleneterephthalate (PET), polyethylene naphthalate (PEN), polyether sulfone(PES), acrylic, or the like can be selected.

The insulating film 1304 is formed using an insulating material such assilicon oxide (SiO_(x)), silicon nitride (SiN_(x)), silicon oxynitride(SiO_(x)N_(y)) (x>y>0), or silicon nitride oxide (SiN_(x)O_(y)) (x>y>0)by a CVD method, a sputtering method, or the like. For example, when theinsulating film 1304 is formed to have a two-layer structure, a siliconnitride oxide film may be formed as a first insulating film and asilicon oxynitride film may be formed as a second insulating film.Alternatively, a silicon nitride film may be formed as a firstinsulating film and a silicon oxide film may be formed as a secondinsulating film. The insulating film 1304 serves as a blocking layer,which prevents an impurity element contained in the substrate 1301 frombeing mixed into elements to be formed over the insulating film 1304. Inthis manner, provision of the insulating film 1304 which serves as theblocking layer can prevent adverse effects on the elements to be formedover the insulating film 1304, which would be caused by an alkali metalsuch as Na or an alkaline earth metal contained in the substrate 1301.Note that when quartz is used as the substrate 1301, the insulating film1304 may be omitted.

The amorphous semiconductor film 1305 is formed with a thickness of 25to 200 nm (preferably, 30 to 150 nm) by a sputtering method, an LPCVDmethod, a plasma CVD method, or the like.

Next, the amorphous semiconductor film 1305 is crystallized by laserlight irradiation. Note that the crystallization of the amorphoussemiconductor film 1305 may also be performed by combining the laserirradiation with a thermal crystallization method using RTA or anannealing furnace, or a thermal crystallization method using a metalelement that promotes the crystallization. After that, the crystallinesemiconductor film is etched into a desired shape, whereby crystallinesemiconductor films 1305 a to 1305 f are formed. Then, a gate insulatingfilm 1306 is formed so as to cover the semiconductor films 1305 a to1305 f (see FIG. 4B).

The gate insulating film 1306 is formed using an insulating materialsuch as silicon oxide, silicon nitride, silicon oxynitride, or siliconnitride oxide by a CVD method, a sputtering method, or the like. Forexample, when the gate insulating film 1306 is formed to have atwo-layer structure, it is preferable to form a silicon oxynitride filmas a first insulating film and form a silicon nitride oxide film as asecond insulating film. Alternatively, it is also preferable to form asilicon oxide film as a first insulating film and form a silicon nitridefilm as a second insulating film.

An example of a manufacturing process of the crystalline semiconductorfilms 1305 a to 1305 f will be briefly described below. First, anamorphous semiconductor film having a thickness of 50 to 60 nm is formedby a plasma CVD method. Next, a solution containing nickel that is ametal element for promoting crystallization is retained on the amorphoussemiconductor film, and dehydrogenation treatment (at 500° C., for onehour) and thermal crystallization treatment (at 550° C., for four hours)are performed on the amorphous semiconductor film; thereby forming acrystalline semiconductor film. After that, the crystallinesemiconductor film is irradiated with laser light, and aphotolithography method is used, so that the crystalline semiconductorfilms 1305 a to 1305 f are formed. Note that without conducting thethermal crystallization using the metal element for promotingcrystallization, the amorphous semiconductor film may be crystallizedonly by laser light irradiation.

As a laser oscillator used for crystallization, either a continuous wavelaser beam (a CW laser beam) or a pulsed laser beam can be used. As alaser beam that can be used here is one or more of followings: gaslasers such as an Ar laser, a Kr laser, and an excimer laser; a laser,using as a medium, single-crystalline YAG, YVO₄, forsterite (Mg₂SiO₄),YAlO₃, or GdVO₄ or polycrystalline (ceramic) YAG, Y₂O₃, YVO₄, YAlO₃, orGdVO₄ which is doped with one or more of Nd, Yb, Cr, Ti, Ho, Er, Tm, andTa as a dopant; a glass laser; a ruby laser; an alexandrite laser; aTi:sapphire laser; a copper vapor laser; and a gold vapor laser. Whenirradiation is performed with the fundamental wave of such a laser beamor the second to fourth harmonics of the fundamental wave, crystals witha large grain size can be obtained. For example, the second harmonic(532 nm) or the third harmonic (355 nm) of an Nd:YVO₄ laser (thefundamental wave of 1064 nm) can be used. In this case, a laser powerdensity of approximately 0.01 to 100 MW/cm² (preferably, 0.1 to 10MW/cm²) is needed, and irradiation is performed at a scanning rate ofapproximately 10 to 2000 cm/sec. It is to be noted that the laser, usingas a medium, single-crystalline YAG, YVO₄, forsterite (Mg₂SiO₄), YAlO₃,or GdVO₄ or polycrystalline (ceramic) YAG, Y₂O₃, YVO₄, YAlO₃, or GdVO₄is doped with one or more of Nd, Yb, Cr, Ti, Ho, Er, Tm, and Ta as adopant; an Ar ion laser; or a Ti:sapphire laser can perform continuousoscillation, whereas it can also be used as pulsed laser at a repetitionrate of 10 MHz or more by conducting a Q-switch operation, mode locking,or the like. When a laser beam is oscillated at a repetition rate of 10MHz or more, a semiconductor film is irradiated with the next pulseduring the period in which the semiconductor film is melted by theprevious laser and solidified. Therefore, unlike the case of using apulsed laser with a low repetition rate, a solid-liquid interface in thesemiconductor film can be continuously moved. Thus, crystal grains growncontinuously in the scanning direction can be obtained.

The gate insulating film 1306 may be formed by oxidation or nitridationof the surfaces of the semiconductor films 1305 a to 1305 f by theabove-described high-density plasma treatment. For example, plasmatreatment with a mixed gas of a rare gas such as He, Ar, Kr, or Xe, andoxygen, nitrogen oxide (NO₂), ammonia, nitrogen, hydrogen, or the likeis used. When plasma is excited by the introduction of microwaves,plasma with a low electron temperature and high density can begenerated. With oxygen radicals (which may include OH radicals) ornitrogen radicals (which may include NH radicals) which are generated bythe high-density plasma, the surfaces of the semiconductor films can beoxidized or nitrided.

By such high-density plasma treatment, an insulating film with athickness of 1 to 20 nm, typically 5 to 10 nm, is formed on thesemiconductor films. Since the reaction in this case is a solid-phasereaction, interface state density between the insulating film and thesemiconductor films can be quite low. Since such high-density plasmatreatment directly oxidizes (or nitrides) the semiconductor films(crystalline silicon or polycrystalline silicon), the insulating filmcan be formed with extremely little variation in thickness ideally. Inaddition, since crystal grain boundaries of crystalline silicon are notstrongly oxidized, an excellent state is obtained. That is, by thesolid-phase oxidation of the surfaces of the semiconductor films byhigh-density plasma treatment which is described here, an insulatingfilm with a uniform thickness and low interface state density can beformed without excessive oxidation reaction at the crystal grainboundaries.

As the gate insulating film 1306, only an insulating film formed byhigh-density plasma treatment may be used, or over the insulating film,an insulating film of silicon oxide, silicon oxynitride, siliconnitride, or the like may be deposited by a CVD method using plasma orthermal reaction to form a stacked layer. In either case, transistorswhich include an insulating film formed by high-density plasma as partor the whole of the gate insulating film can have less characteristicvariation.

In addition, the semiconductor films 1305 a to 1305 f, which areobtained by irradiation of the semiconductor film 1305 with a continuouswave laser or a laser beam oscillated at a repetition rate of 10 MHz ormore and scanning of the semiconductor film in one direction tocrystallize the semiconductor film, have a characteristic that crystalsgrow in the beam scanning direction. A transistor is arranged so thatits channel length direction (direction in which carriers move when achannel formation region is formed) is aligned with the scanningdirection, and the above-described gate insulating film is combined,whereby a thin film transistor (TFTs) with high electron field effectmobility and few variations in characteristics can be obtained.

Note that in this embodiment, an impurity element is introduced to thesemiconductor film 1305 f in order to use the semiconductor film 1305 fas an electrode of a capacitor element. Specifically, before or afterthe formation of the gate insulating film 1306, the semiconductor films1305 a to 1305 e are covered with a resist, and an n-type or p-typeimpurity element can be selectively introduced to the semiconductor film1305 f by an ion doping method or an ion implantation method. As ann-type impurity element, phosphorus (P), arsenic (As), or the like canbe used. As a p-type impurity element, boron (B), aluminum (Al), gallium(Ga), or the like can be used. Here, phosphorus (P) is used as animpurity element imparting n-type conductivity and is selectivelyintroduced to the semiconductor film 1305 f.

Next, a first conductive film and a second conductive film are stackedover the gate insulating film 1306. Here, the first conductive film isformed to have a thickness of 20 to 100 nm by a CVD method, a sputteringmethod, or the like. The second conductive film is formed to have athickness of 100 to 400 nm. The first conductive film and the secondconductive film are formed of an element selected from tantalum (Ta),tungsten (W), titanium (Ti), molybdenum (Mo), aluminum (Al), copper(Cu), chromium (Cr), niobium (Nb), or the like, or an alloy material ora compound material containing the element as its main component.Alternatively, the first conductive film and the second conductive filmare formed of semiconductor materials typified by polycrystallinesilicon doped with an impurity element such as phosphorus. As acombination example of the first conductive film and the secondconductive film, a tantalum nitride film and a tungsten film; a tungstennitride film and a tungsten film; a molybdenum nitride film and amolybdenum film; and the like can be given. Tungsten and tantalumnitride have high heat resistance. Therefore, after forming the firstconductive film and the second conductive film, thermal treatment forthe purpose of heat activation can be applied thereto. In addition, inthe case where a two-layer structure is not employed, but a three-layerstructure is employed, it is preferable to use a stacked structure of amolybdenum film, an aluminum film, and a molybdenum film.

Next, a mask is formed of a resist using photolithography, and etchingtreatment for forming gate electrodes and gate lines is conducted. Thus,gate electrodes 1307 are formed over the semiconductor films 1305 a to1305 f. Here, a stacked structure of first conductive films 1307 a andsecond conductive films 1307 b is shown as an example of the gateelectrode 1307.

Next, the semiconductor films 1305 a to 1305 f are doped with an n-typeimpurity element at low concentration, by an ion doping method or an ionimplantation method using the gate electrodes 1307 as masks. Then, maskformed of a resist is selectively formed by photolithography, and thesemiconductor films 1305 a to 1305 f are doped with a p-type impurityelement at high concentration. As an n-type impurity element, phosphorus(P), arsenic (As), or the like can be used. As a p-type impurityelement, boron (B), aluminum (Al), gallium (Ga), or the like can beused. Here, phosphorus (P) is used as an n-type impurity element and isselectively introduced into the semiconductor films 1305 a to 1305 fusing the gate electrodes 1307 as masks so as to be contained atconcentrations of 1×10¹⁵ to 1×10¹⁹/cm³. Thus, n-type impurity regions1308 are formed. Then, the semiconductor films 1305 a, 1305 b, 1305 d,and 1305 f are covered with a resist, and boron (B) is used as a p-typeimpurity element and is selectively introduced into the semiconductorfilms 1305 c and 1305 e so as to be contained at concentrations of1×10¹⁹ to 1×10²⁰/cm³. Thus, n-type impurity regions 1309 are formed (seeFIG. 4C).

Subsequently, an insulating film is formed so as to cover the gateinsulating film 1306 and the gate electrodes 1307. The insulating filmis formed to have either a single layer or a stacked layer of a filmcontaining an inorganic material such as silicon, silicon oxide, orsilicon nitride, or a film containing an organic material such as anorganic resin by a plasma CVD method, a sputtering method, or the like.Next, the insulating film is selectively etched by anisotropic etchingwhich etches mainly in the perpendicular direction, so that insulatingfilms 1310 (also referred to as sidewalls) which are in contact with theside surfaces of the gate electrodes 1307 are formed. The insulatingfilms 1310 are used as doping masks for forming LDD (lightly DopedDrain) regions.

Next, the semiconductor films 1305 a, 1305 b, 1305 d, and 1305 f aredoped with an n-type impurity element at high concentrations, using amask formed of a resist by photolithography method and using the gateelectrodes 1307 and the insulating films 1310 as masks. Thus, n-typeimpurity regions 1311 are formed. Here, phosphorus (P) is used as then-type impurity element, and is selectively introduced into thesemiconductor films 1305 a, 1305 b, 1305 d, and 1305 f so as to becontained at concentrations of 1×10¹⁹ to 1×10²⁰/cm³. Thus, the n-typeimpurity regions 1311 with higher concentrations of impurity than thoseof the impurity regions 1308 are formed.

Through the above steps, n-channel transistors 1300 a, 1300 b, and 1300d; p-channel thin film transistors 1300 c and 1300 e; and a capacitorelement 1300 f are formed (see FIG. 4D).

In the n-channel thin film transistor 1300 a, a channel formation regionis formed in a region of the semiconductor film 1305 a, which overlapswith the gate electrode 1307; the impurity regions 1311 which form asource region and a drain region are formed in regions which do notoverlap with the gate electrode 1307 and the insulating films 1310; anda low concentration impurity regions (LDD regions) are formed in regionswhich overlap with the insulating films and between the channelformation region and each of the impurity region 1311. Similarly,channel formation regions, low concentration impurity regions, and theimpurity regions 1311 are formed in the n-channel thin film transistors1300 b and 1300 d.

In the p-channel thin film transistor 1300 c, a channel formation regionis formed in a region of the semiconductor film 1305 c, which overlapswith the gate electrode 1307; and the impurity regions 1309 which form asource region and a drain region are formed in regions which do notoverlap with the gate electrode 1307. Similarly, a channel formationregion and the impurity regions 1309 are formed in the p-channel thinfilm transistor 1300 e. Here, although LDD regions are not formed in thep-channel thin film transistors 1300 c and 1300 e, LDD regions may beprovided in the p-channel thin film transistors or a structure withoutLDD regions may be applied to the n-channel thin film transistors.

Next, an insulating film with a single layer structure or a stackedstructure is formed so as to cover the semiconductor films 1305 a to1305 f, the gate electrodes 1307, and the like. Then, conductive films1313 electrically connected to the impurity regions 1309 and 1311 whichform the source and drain regions of the thin film transistors 1300 a to1300 e, and one electrode of the capacitor element 1300 f are formedover the insulating film (see FIG. 5A). The insulating film is formed ofa single layer or a stacked layer, using an inorganic material such assilicon oxide or silicon nitride, an organic material such as polyimide,polyamide, benzocyclobutene, acrylic, or epoxy, a siloxane material, orthe like by a CVD method, a sputtering method, an SOG method, a dropletdischarging method, a screen printing method, or the like. Here, theinsulating film is formed to have two layers, and a silicon nitrideoxide film is formed as a first insulating film 1312 a and a siliconoxynitride film is formed as a second insulating film 1312 b. Inaddition, the conductive films 1313 can form the source and drainelectrodes of the thin film transistors 1300 a to 1300 e. Note that asiloxane material corresponds to a material having a Si—O—Si bond.Siloxane has a skeletal structure formed of bonds of silicon (Si) andoxygen (O). As a substituent, an organic group containing at leasthydrogen (for example, an alkyl group or aromatic hydrocarbon) is used.A fluoro group can also be used as a substituent. Alternatively, anorganic group containing at least hydrogen and a fluoro group may beused as a substituent.

It is to be noted that before the insulating films 1312 a and 1312 b areformed or after one or a plurality of them is/are formed, heat treatmentis preferably applied in order to recover the crystallinity of thesemiconductor films, to activate the impurity element which has beenadded into the semiconductor films, or to hydrogenate the semiconductorfilms. As the heat treatment, thermal annealing, laser annealing, RTA,or the like is preferably applied.

The conductive films 1313 are formed of a single layer or a stackedlayer of an element selected from aluminum (Al), tungsten (W), titanium(Ti), tantalum (Ta), molybdenum (Mo), nickel (Ni), platinum (Pt), copper(Cu), gold (Au), silver (Ag), manganese (Mn), neodymium (Nd), carbon(C), or silicon (Si), or an alloy material or a compound materialcontaining the element as its main component. An alloy materialcontaining aluminum as its main component corresponds to, for example, amaterial which contains aluminum as its main component and also containsnickel, or a material which contains aluminum as its main component andalso contains nickel and one or both of carbon and silicon. Theconductive films 1313 are preferably formed to have a stacked structureof a barrier film, an aluminum-silicon film, and a barrier film or astacked structure of a barrier film, an aluminum silicon film, atitanium nitride film, and a barrier film. It is to be noted that the“barrier film” corresponds to a thin film formed of titanium, titaniumnitride, molybdenum, or molybdenum nitride. Aluminum and aluminumsilicon are the most suitable material for forming the conductive films1313 because they have low resistance value and are inexpensive. Whenbarrier layers are provided as the top layer and the bottom layer,generation of hillocks of aluminum or aluminum silicon can be prevented.In addition, when a barrier film formed of titanium which is an elementhaving a high reducing property is formed, even when there is a thinnatural oxide film formed on the crystalline semiconductor film, thenatural oxide film can be chemically reduced, and a favorable contactwith the crystalline semiconductor film can be obtained.

Next, an insulating film 1314 is formed so as to cover the conductivefilms 1313, and a conductive film 1316 that is electrically connected tothe conductive films 1313 which form the source electrode or the drainelectrode of the thin film transistor 1300 a is formed over theinsulating film 1314. The conductive film 1316 may be formed using anyof the above-described materials which have been described for theconductive films 1313.

Next, a conductive film 1317 functioning as an antenna is formed so asto be electrically connected to the conductive film 1316 (see FIG. 5B).

The insulating film 1314 can be formed of a single layer or a stackedlayer of an insulating film, containing oxygen or nitrogen, of siliconoxide, silicon nitride, silicon oxynitride, silicon nitride oxide, orthe like; a film containing carbon such as DLC (Diamond-Like Carbon); anorganic material such as epoxy, polyimide, polyamide, polyvinyl phenol,benzocyclobutene, or acrylic; or a siloxane material such as a siloxaneresin.

The conductive film 1317 can be formed of a conductive material by a CVDmethod, a sputtering method, a printing method such as screen printingor gravure printing, a droplet discharging method, a dispenser method, aplating method, or the like. The conductive film 1317 is formed of asingle layer or a stacked layer of an element selected from aluminum(Al), titanium (Ti), silver (Ag), copper (Cu), gold (Au), platinum (Pt),nickel (Ni), palladium (Pd), tantalum (Ta), or molybdenum (Mo), or analloy material or a compound material containing the element as its maincomponent.

For example, when the conductive film 1317 functioning as an antenna isformed by a screen printing method, the antenna can be provided byselective printing of a conductive paste in which conductive particleswith a grain diameter of several nm to several tens of μm are dissolvedor dispersed in an organic resin. The conductive particles can be atleast one or more of metal particles selected from silver (Ag), gold(Ag), copper (Cu), nickel (Ni), platinum (Pt), palladium (Pd), tantalum(Ta), molybdenum (Mo), titanium (Ti), or the like; fine particles ofsilver halide; and dispersive nanoparticles. In addition, the organicresin included in the conductive paste can be one or more of organicresins which function as a binder, a solvent, a dispersing agent, or acoating material of the metal particles. Typically, an organic resinsuch as an epoxy resin and a silicone resin can be given. In addition,it is preferable to form the conductive film by the steps of providing aconductive paste and baking it. For example, in the case of using fineparticles (e.g., a grain diameter of 1 to 100 nm) containing silver asits main component as a material of the conductive paste, the conductivepaste is baked and hardened at temperatures in the range of 150 to 300°C. so that the conductive film can be obtained. Alternatively, it isalso possible to use fine particles containing solder or lead-freesolder as its main component. In that case, fine particles with a graindiameter of less than or equal to 20 μm are preferably used. Solder andlead-free solder have the advantage of low cost.

In addition, in this embodiment, an antenna is formed of conductive film1317 directly over the insulating film 1314 by patterning or screenprinting after the film formation; however, the antenna may be formedover another substrate such as the substrate described above, a plasticsubstrate which is flexible, or the like and may be connected andattached so as to be electrically connected to the conductive film 1316.

Finally, the substrate is cut by dicing in a desired shape and size, sothat a semiconductor device can be completed.

Note that in the semiconductor device shown in this embodiment, thestructure of a transistor can have various modes. The structure of atransistor is not limited to the particular structure shown in thisembodiment. For example, a multi-gate structure provided with two ormore gate electrodes may be used. With the multi-gate structure, channelregions are connected in series. Thus, a structure is obtained, in whicha plurality of transistors are connected in series. By employing themulti-gate structure, an off current can be reduced, reliability can beenhanced by improving a withstand voltage of the transistor, flatcharacteristics can be obtained, in which a drain-source current is notchanged so much even if a drain-source voltage is changed when thetransistor is operated in a saturation region, and so on. Alternatively,a structure may be employed, in which gate electrodes are arranged aboveand below a channel. By employing the structure where gate electrodesare arranged above and below a channel, a channel region is increased;therefore, a current value can be increased and a subthreshold swing canbe improved because a depletion layer is easily generated. When gateelectrodes are arranged above and below a channel, a structure isobtained, in which a plurality of transistors are connected in parallel.

Further alternatively, the following structure may be employed: astructure where a gate electrode is arranged above a channel, astructure where a gate electrode is arranged below a channel, astaggered structure, or an inversely staggered structure. A channelregion may be divided into a plurality of regions, and the plurality ofchannel regions may be connected to each other in parallel or in series.Further, a source electrode or a drain electrode may be overlapped witha channel (or part thereof). By employing the structure where a sourceelectrode or a drain electrode is overlapped with a channel (or partthereof), instability of an operation due to electric chargeaccumulation in part of a channel can be prevented. In addition, an LDDregion may be provided. By providing the LDD region, an off current canbe reduced, reliability can be enhanced by improving a withstand voltageof the transistor, and flat characteristics can be obtained, in which adrain-source current is not changed so much even if a drain-sourcevoltage is changed when the transistor is operated in a saturationregion.

Note that the transistors which can be used in the present inventionincludes a transistor formed using single crystalline silicon, atransistor using SOI, and the like, in addition to a thin filmtransistor using a polycrystalline semiconductor, a microcrystallinesemiconductor, or an amorphous semiconductor. Alternatively, atransistor using an organic semiconductor, or a transistor using acarbon nanotube may be used.

Note that a manufacture method shown in this embodiment can be appliedto semiconductor devices of any of the embodiment modes, which aredescribed in this specification.

EMBODIMENT 2

This embodiment will describe the case in which elements such as thinfilm transistors and the like are transferred to a flexible substrate,after the elements are formed over a supporting substrate in accordancewith the process of Embodiment 1.

As shown FIG. 6A, a separation layer 1303 is formed over the substrate1301 with an insulating film 1302 interposed therebetween. Then, anelement group such as thin film transistors is formed over the substrate1301 in accordance with the process of Embodiment 1.

The insulating film 1302 is formed using an insulating material such assilicon oxide (SiO_(x)), silicon nitride (SiN_(x)), silicon oxynitride(SiO_(x)N_(y)) (x>y>0), or silicon nitride oxide (SiN_(x)O_(y)) (x>y>0)by a CVD method, a sputtering method, or the like. The insulating film1302 functions as a blocking layer which prevents an impurity elementcontained in the substrate 1301 from being mixed into the separationlayer 1303 or elements to be formed thereover. In this manner, provisionof the insulating film 1302 which functions as the blocking layer canprevent adverse effects on the elements to be formed over the separationlayer 1303, cased by an alkali metal such as Na or an alkaline earthmetal contained in the substrate 1301. It is to be noted that whenquartz is used for the substrate 1301, the insulating film 1302 may beomitted.

The separation layer 1303 can be formed using a metal film, a stackedstructure of a metal film and a metal oxide film, or the like. As themetal film, either a single layer or stacked layers are formed using anelement selected from tungsten (W), molybdenum (Mo), titanium (Ti),tantalum (Ta), niobium (Nb), nickel (Ni), cobalt (Co), zirconium (Zr),zinc (Zn), ruthenium (Ru), rhodium (Rh), palladium (Pd), osmium (Os), oriridium (Ir), or an alloy material or a compound material containing theelement as its main component. In addition, such materials can be formedby a sputtering method, various CVD methods such as a plasma CVD method,or the like. A stacked structure of a metal film and a metal oxide filmcan be obtained by the steps of forming the above-described metal film,and conducting plasma treatment thereto under an oxygen atmosphere or anN₂O atmosphere or conducting heat treatment thereto under an oxygenatmosphere or an N₂O atmosphere, thereby forming oxide or oxynitride ofthe metal film on the surface of the metal film. For example, when atungsten film is provided as a metal film by a sputtering method, a CVDmethod, or the like, a metal oxide film formed of tungsten oxide can beformed on the surface of the tungsten film by conducting of plasmatreatment to the tungsten film. In that case, the tungsten oxide can berepresented by WO_(x), where x is in the range of 2 to 3. For example,there are cases where x is 2 (WO₂), x is 2.5 (W₂O₅), x is 2.75 (W₄O₁₁),x is 3 (WO₃), and the like. When forming tungsten oxide, there is noparticular limitation on the value of x, and thus, which of the aboveoxides is to be formed may be determined base on the etching rate of thelike. In addition, after a metal film (e.g., tungsten) is formed, aninsulating film formed of silicon oxide or the like may be formed overthe metal film by a sputtering method, and also metal oxide (e.g.,tungsten oxide over tungsten) may be formed over the metal film.

Next, after forming an insulating film 1318 so as to cover theconductive film 1317, layers including the thin film transistors 1300 ato 1300 e, the capacitor element 1300 f, the conductive film 1317, andthe like (hereinafter referred to as an “element formation layer 1319”)are peeled off the substrate 1301. Here, after forming openings in aportion of the element formation layer 1319, where the thin filmtransistors 1300 a to 1300 e and the capacitor element 1300 f are notincluded, by laser light irradiation (e.g., UV light) (see FIG. 6A), theelement formation layer 1319 can be peeled off the substrate 1301 with aphysical force. Note that element formation layer 1319 can be peeled offwith a liquid such as water so as to prevent the thin film transistorsprovided in the element formation layer 1319 from being broken by staticelectricity. Further, the substrate 1301 that is peeled off the elementformation layer 1319, the cost can be reduced.

The insulating film 1318 can be formed of a single layer or a stackedlayer of an insulating film, containing oxygen or nitrogen, of siliconoxide, silicon nitride, silicon oxynitride, silicon nitride oxide, orthe like; a film containing carbon such as DLC (Diamond-Like Carbon); anorganic material such as epoxy, polyimide, polyamide, polyvinyl phenol,benzocyclobutene, or acrylic; or a siloxane material such as a siloxaneresin by a CVD method, a sputtering method, or the like.

In this embodiment, after forming the openings in the element formationlayer 1319 by laser light irradiation, a first sheet material 1320 isattached to one surface of the element formation layer 1319 (the surfacewhere the insulating film 1318 is exposed), and then the elementformation layer 1319 is peeled off the substrate 1301 (see FIG. 6B).

After that, it is preferable that a second sheet material (not shown) isattached to a separation layer (the surface exposed by peeling), andthen, one or both of heat treatment and pressure treatment is performedto attach the second sheet material to the separation layer. As thefirst sheet material and the second sheet material, a hot-melt film orthe like can be used.

Additionally, a film to which antistatic treatment for preventing staticelectricity or the like has been subjected (hereinafter referred to asan antistatic film) can be used. As examples of the antistatic film, afilm in which an antistatic material is dispersed in a resin, a film towhich an antistatic material is attached, and the like can be given. Thefilm provided with an antistatic material can be a film with anantistatic material provided over one of its surfaces, or a film with anantistatic material provided over both of its surfaces. The film with anantistatic material provided over one of its surfaces may be attached tothe layer so that the surface provided with the antistatic material isplaced on the inner side of the film or the outer side of the film. Theantistatic material may be provided over the entire surface of the film,or over part of the film. As an antistatic material, a metal, indium tinoxide (ITO), or a surfactant such as an amphoteric surfactant, acationic surfactant, or a nonionic surfactant can be used. In addition,as an antistatic material, a resin material which contains across-linked copolymer having a carboxyl group and a quaternary ammoniumbase on its side chain, or the like can be used. Such a material can beattached, mixed, or applied to a film, so that an antistatic film can beformed. By sealing with the antistatic film the semiconductor elementscan be suppressed from adverse effects such as external staticelectricity when dealt with as a commercial product.

Although a circuit can be formed over an insulating substrate using athin film transistor using a manufacturing process shown in Embodiment 1or this embodiment, a thin film transistor in general tends to havelower mobility and large variation in threshold voltage becausecrystalline state of a thin film transistor is inferior to that of atransistor formed over a single crystal substrate or a transistor formedover an SOI substrate. Thus, as described above, when the AC voltagewhich is generated by reception of the carrier waves is rectified so asto ensure a power supply for driving an internal circuit, loss of theinternal electric power generated from the received power becomes large.Therefore, by employing the present invention, even a circuit formedusing a thin film transistor can generate a high voltage easily withreduced loss.

Note that the manufacturing process of a semiconductor device shown inthis embodiment can be applied to semiconductor devices of otherembodiment modes and an embodiment which are described in thisspecification.

This application is based on Japanese Patent Application serial No.2007-002072 filed with Japan Patent Office on Jan. 10, 2007, the entirecontents of which are hereby incorporated by reference.

What is claimed is:
 1. A semiconductor device comprising: an antennaconfigured to generate an AC voltage from carrier waves; a rectifiercircuit configured to generate and output a DC voltage from the ACvoltage; a function portion configured to conduct processing in responseto a command included in the carrier waves; and a storage capacitorportion configured to store the DC voltage output from the rectifiercircuit, the storage capacitor portion comprising: a first terminalconnected to the rectifier circuit and to the function portion; a secondterminal; first to n-th capacitor elements; and a plurality of switches,wherein the plurality of switches are configured to connect the first ton-th capacitor elements in parallel between the first terminal and thesecond terminal, in a first mode, wherein the plurality of switches areconfigured to connect the first to m-th capacitor elements in seriesbetween the first terminal and the second terminal, in a second mode,wherein n is natural number larger than 1, wherein m is natural numberlarger than 1 and smaller than or equal to n, wherein a potential of thesecond terminal is fixed, and wherein a switch is connected between thefirst terminal and the rectifier circuit.
 2. The semiconductor deviceaccording to claim 1, further comprising: a substrate having aninsulating surface, wherein the rectifier circuit comprises a thin filmtransistor over the substrate.
 3. The semiconductor device according toclaim 1, further comprising: a substrate having an insulating surface,wherein the storage capacitor portion comprises a thin film transistorover the substrate.
 4. The semiconductor device according to claim 1,further comprising: a substrate having an insulating surface, whereinthe antenna is formed over the substrate.
 5. The semiconductor deviceaccording to claim 1, wherein the function portion comprises arewritable memory element group, and wherein the plurality of switchesare configured to enter the second mode when a data included in thecarrier waves is written in the rewritable memory element group.
 6. Asemiconductor device comprising: an antenna configured to generate an ACvoltage from carrier waves; a rectifier circuit configured to generateand output a DC voltage from the AC voltage; a function portionconfigured to conduct processing in response to a command included inthe carrier waves; and a storage capacitor portion configured to storethe DC voltage output from the rectifier circuit, the storage capacitorportion comprising: a first terminal connected to the rectifier circuitand to the function portion; a second terminal; first to n-th capacitorelements; and a plurality of switches, wherein the plurality of switchesare configured to connect the first to n-th capacitor elements inparallel between the first terminal and the second terminal, in a firstmode, wherein the plurality of switches are configured to connect thefirst to n-th capacitor elements in series between the first terminaland the second terminal, in a second mode, wherein n is natural numberlarger than 1, wherein a potential of the second terminal is fixed, andwherein a switch is connected between the first terminal and therectifier circuit.
 7. The semiconductor device according to claim 6,further comprising: a substrate having an insulating surface, whereinthe rectifier circuit comprises a thin film transistor over thesubstrate.
 8. The semiconductor device according to claim 6, furthercomprising: a substrate having an insulating surface, wherein thestorage capacitor portion comprises a thin film transistor over thesubstrate.
 9. The semiconductor device according to claim 6, furthercomprising: a substrate having an insulating surface, wherein theantenna is formed over the substrate.
 10. The semiconductor deviceaccording to claim 6, wherein the function portion comprises arewritable memory element group, and wherein the plurality of switchesare configured to enter the second mode when a data included in thecarrier waves is written in the rewritable memory element group.
 11. Asemiconductor device comprising: an antenna configured to generate an ACvoltage from carrier waves; a rectifier circuit configured to generateand output a DC voltage from the AC voltage; a first function portionconfigured to conduct first processing in response to a first commandincluded in the carrier waves; a second function portion configured toconduct second processing in response to a second command included inthe carrier waves; a first storage capacitor portion configured to storethe DC voltage output from the rectifier circuit, the first storagecapacitor portion comprising: a first terminal connected to therectifier circuit and to the first function portion; a second terminal;first to n-th capacitor elements; and a plurality of switches, and asecond storage capacitor portion configured to store the DC voltage;wherein the plurality of switches are configured to connect the first ton-th capacitor elements in parallel between the first terminal and thesecond terminal, in a first mode, wherein the plurality of switches areconfigured to connect the first to m-th capacitor elements in seriesbetween the first terminal and the second terminal, in a second mode,wherein the second storage capacitor portion is connected between therectifier circuit and the second function portion, wherein n is naturalnumber larger than 1, wherein m is natural number larger than 1 andsmaller than or equal to n, wherein a potential of the second terminalis fixed, and wherein a switch is connected between the first terminaland the rectifier circuit.
 12. The semiconductor device according toclaim 11, further comprising: a substrate having an insulating surface,wherein the rectifier circuit comprises a thin film transistor over thesubstrate.
 13. The semiconductor device according to claim 11, furthercomprising: a substrate having an insulating surface, wherein at leastone of the first storage capacitor portion and the second storagecapacitor portion comprises a thin film transistor over the substrate.14. The semiconductor device according to claim 11, further comprising:a substrate having an insulating surface, wherein the antenna is formedover the substrate.
 15. The semiconductor device according to claim 11,wherein the first function portion comprises a rewritable memory elementgroup, and wherein the plurality of switches are configured to enter thesecond mode when a data included in the carrier waves is written in therewritable memory element group.
 16. A semiconductor device comprising:an antenna configured to generate an AC voltage from carrier waves; arectifier circuit configured to generate and output a DC voltage fromthe AC voltage; a first function portion configured to conduct firstprocessing in response to a first command included in the carrier waves;a second function portion configured to conduct second processing inresponse to a second command included in the carrier waves; a firststorage capacitor portion configured to store the DC voltage output fromthe rectifier circuit, the first storage capacitor portion comprising: afirst terminal connected to the rectifier circuit and to the firstfunction portion; a second terminal; first to n-th capacitor elements;and a plurality of switches, and a second storage capacitor portionconfigured to store the DC voltage; wherein the plurality of switchesare configured to connect the first to n-th capacitor elements inparallel between the first terminal and the second terminal, in a firstmode, wherein the plurality of switches are configured to connect thefirst to n-th capacitor elements in series between the first terminaland the second terminal, in a second mode, wherein the second storagecapacitor portion is connected between the rectifier circuit and thesecond function portion, wherein n is natural number larger than 1,wherein a potential of the second terminal is fixed, and wherein aswitch is connected between the first terminal and the rectifiercircuit.
 17. The semiconductor device according to claim 16, furthercomprising: a substrate having an insulating surface, wherein therectifier circuit comprises a thin film transistor over the substrate.18. The semiconductor device according to claim 16, further comprising:a substrate having an insulating surface, wherein at least one of thefirst storage capacitor portion and the second storage capacitor portioncomprises a thin film transistor over the substrate.
 19. Thesemiconductor device according to claim 16, further comprising: asubstrate having an insulating surface, wherein the antenna is formedover the substrate.
 20. The semiconductor device according to claim 16,wherein the first function portion comprises a rewritable memory elementgroup, and wherein the plurality of switches are configured to enter thesecond mode when a data included in the carrier waves is written in therewritable memory element group.
 21. A semiconductor device comprising:an antenna configured to generate an AC voltage from carrier waves; arectifier circuit configured to generate and output a DC voltage fromthe AC voltage; a first function portion configured to conduct firstprocessing in response to a first command included in the carrier waves;a second function portion configured to conduct second processing inresponse to a second command included in the carrier waves; a firststorage capacitor portion configured to store the DC voltage output fromthe rectifier circuit, the first storage capacitor portion comprising: afirst terminal connected to the rectifier circuit and to the firstfunction portion; a second terminal; first to n-th capacitor elements;and a plurality of switches, and a second storage capacitor portionconfigured to store the DC voltage, the second storage capacitor portioncomprising: a third terminal connected to the rectifier circuit and tothe second function portion; a fourth terminal; and plurality ofcapacitor elements connected in parallel between the third terminal andthe fourth terminal; wherein the plurality of switches are configured toconnect the first to n-th capacitor elements in parallel between thefirst terminal and the second terminal, in a first mode, wherein theplurality of switches are configured to connect the first to m-thcapacitor elements in series between the first terminal and the secondterminal, in a second mode, wherein n is natural number larger than 1,wherein m is natural number larger than 1 and smaller than or equal ton, wherein a potential of the second terminal is fixed, and wherein aswitch is connected between the first terminal and the rectifiercircuit.
 22. The semiconductor device according to claim 21, furthercomprising: a substrate having an insulating surface, wherein therectifier circuit comprises a thin film transistor over the substrate.23. The semiconductor device according to claim 21, further comprising:a substrate having an insulating surface, wherein at least one of thefirst storage capacitor portion and the second storage capacitor portioncomprises a thin film transistor over the substrate.
 24. Thesemiconductor device according to claim 21, further comprising: asubstrate having an insulating surface, wherein the antenna is formedover the substrate.
 25. The semiconductor device according to claim 21,wherein the first function portion comprises a rewritable memory elementgroup, and wherein the plurality of switches are configured to enter thesecond mode when a data included in the carrier waves is written in therewritable memory element group.